Users especially of FM radio devices know that the FM radio reception is sometimes disturbed due to so called multipath or fading effects. These disturbing effects usually originate from the fact that both a direct wave and a reflected wave from a transmitter are reaching the radio receiver and both signals are almost identical but show a time shift which finally leads to an audible disturbance.
Within auto mobile applications mobile signal reception is provided. Especially for mobile signal reception the signal disturbances are changing in time since the conditions are changing during e.g. driving of a car. While the car is moving the paths which the radio waves are taking to reach the antenna or the receiver are varying and therefore the conditions and the signal disturbances are changing quickly. Accordingly an at least almost constant change in time of the signal strength and of the relative phase of the direct signal and of the reflected signal is at last almost constantly changing. Accordingly the perceived disturbances of the signal are changing with time.
When receiving FM broadcast signals using a receiver, a mechanism is commonly used to detect the above mentioned signal disturbances. Since the disturbances can be detected measures are taken to act on the outcome of these detected disturbances e.g. by changing parameters that control the audio bandwidth, that reduce the stereo content, etc., in order to obtain a better perceived audio signal quality. This method of detecting the above mentioned disturbances of FM signals, and the method to improve the perceived audio quality is often referred to as ‘weak signal handling’.
The weak signal handling shows a major drawback which is related to the speed of change at which the various control parameters can be changed. This speed of change is a critical measure with regard to the perceived audio quality. This speed of change has to be fast enough to cope with the time-varying disturbances, while the speed of change cannot be that fast that the fast changing of parameters itself leads to noticeable signal distortions.
EP 1394955 B1 discloses a system for receiving composite signal including a main component and a multi-path component in which a controller creates a phase error signal.
EP 1909398 A1 discloses an apparatus for suppressing the presence of multi-path propagation in a modulated digital signal which creates a derivative signal and applies a non-linear Teager-Kaiser function to said digital signal.
Furthermore US 2006/0040627 A1 discloses an apparatus for improving sound quality from degradation due to multi-path noise in which an arithmetic unit subtracts a signal based on the detection signal of multi-path noise.
All the above mentioned systems according to the prior art show drawbacks with regard to timing of fast changing disturbances which spoil the over all signal quality.